1. Technical Field
The present disclosure relates to a mechanism for controlling the operable inside diameter of a passageway through a valve assembly of a trocar housing. More particularly, the present disclosure relates to a diameter reduction structure that restricts the movement of small surgical instruments and accommodates large diameter surgical instruments in the passageway of a trocar housing to facilitate the maintenance of a gas tight seal formed by the valve assembly.
2. Background of Related Art
Trocar valve assemblies preferably provide a fluid tight seal about a surgical instrument introduced through the trocar during a minimally invasive surgical procedure. A typical valve assembly includes an outer seal, which can be fixed or floating, in combination with additional inner seals. Fixed outer seals are limited by their ability to sustain a seal when a smaller surgical instrument is moved off-axis relative to a central axis of the trocar. Fixed seals are also limited by their ability to sustain their integrity when the surgical instrument is angulated. Such extreme ranges of motion of smaller diameter surgical instruments within the cannula can create a “cat eye” or crescent shaped gap in the fixed seal that can result in a loss of seal integrity. Additional problems include the flexibility of the seal in maintaining its integrity when both small diameter and large diameter surgical instruments are used.
Devices to restrict the diameter of a passageway in a trocar housing generally require an additional mechanism to be positioned on the proximal end of the trocar housing that restricts the range of motion of small surgical instruments. These diameter reducing devices, however, typically employ additional seals and/or structures that require adjustments by the user to accommodate different sized surgical instruments, thereby complicating the surgical process.
A continuing need exists for a diameter reducing structure that can limit parallel off-axis as well as angular movements of small diameter surgical instruments and accommodate larger diameter surgical instruments without external adjustments.